Changes:
- pkg register checks conflicts before installing the files
- do not provide any shlibs if the "no_provide_shlib" annotation is set
- fix invalid free() in keywords arguments parsing
- Add ability to select usage of IPv4/IPv6 via config, repository config or command line
- some documentation fixes and improvements
- If one of -P, -I or -R is not explicitly given on the command line, do
not emit error messages while searching for a mechanism to find data
about the latest available ports.
- Rework automatic directory deletion
